Modelling of several aspects of muscle contraction is presently underway. First, we are quantitatively modelling our new cross-bridge model which is based on the concept that the myosin cross-bridge oscillates between states weakly bound to actin with a preferred angle of about 90 degrees and states strongly bound to actin with a preferred angle of about 45 degrees. The former states have bound ATP or ADP plus Pi while the latter states have no bound Pi. The concept of two major types of cross-bridge states is combined with the biochemical concept or rapid equilibria between attached and detached states and the physiological concept of an elastic cross-bridge to allow a model in which the myosin does not detach from actin during each cycle of cross-bridge action but does mechanically detach when the muscle is shortening. In addition to modelling cross-bridge actin in vivo, we are currently modelling the cooperative actions of the troponin-tropomyosin-actin complex which we have observed in our experimental work. This involves detailed modelling of the cooperative binding of myosin-ADP to the troponin-tropomyosin-actin complex, a phenomenon which we have observed in our experimental work. It also involves modelling the cooperative effects of troponin-tropomyosin on the steady-state actin-activated myosin ATPase activity.